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Aberrant lysosomal carbohydrate storage accompanies endocytic defects and neurodegeneration in Drosophila benchwarmer.

Dermaut B, Norga KK, Kania A, Verstreken P, Pan H, Zhou Y, Callaerts P, Bellen HJ - J. Cell Biol. (2005)

Bottom Line: Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions.Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner.We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT
Lysosomal storage is the most common cause of neurodegenerative brain disease in preadulthood. However, the underlying cellular mechanisms that lead to neuronal dysfunction are unknown. Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions. At the bnch larval neuromuscular junction, we observe similar inclusions and find defects in synaptic vesicle recycling at the level of endocytosis. In addition, loss of bnch slows endosome-to-lysosome trafficking in larval garland cells. In adult bnch flies, we observe age-dependent synaptic dysfunction and neuronal degeneration. Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner. We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

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bnch loss of function alleles are semi-lethal and disrupt a highly conserved predicted anion/sugar permease of the MFS. (A) The genomic bnch locus (52E, 14 kb) encodes at least five alternatively spliced transcripts. Translation initiation and termination sites are indicated in red. The approximate location of the P{lacW}[25/11] insertion and point mutations (11F5, E14.1, N, P) is shown. The extent of small deletions (Δ29, Δ31, Δ86) generated by imprecise P-element excision of P{LacW}[25/11] is indicated. The alleles affect gene regions that are common to all alternatively spliced isoforms. (B) Predicted membrane topology for Bnch showing the 12 transmembrane domains typical for proteins of the MFS. The position of the anion/cation (ACS) domain signature is indicated in red. EMS mutations result in the introduction of stop codons (for 11F5, E14.1, and P) or a nonconservative amino acid change (for N) and their positions in the protein are indicated by asterisks. The position of the N missense mutation is shown in a partial multiple alignment of eukaryotic Bnch proteins and consensus sequences of the ACS and sugar porter (SP) subfamilies. The percentages identity and similarity of eukaryotic Bnch proteins to Drosophila Bnch are given in the table. Number of identified Bnch homologues per species is between parentheses. (C) Complementation analysis of bnch point mutations (11F5, E14.1, N, P), excision alleles (Δ29, Δ31, Δ86), deletions (Δ2B, Jp8) and P-element insertion (25/11) indicates allelism. The P{LacW}[25/11] chromosome and its derivatives contain an unrelated lethal mutation that is uncovered by the Jp8 deficiency. The frequency of homozygous and transheterozygous escapers (in parentheses) is not absolute and strongly dependent on the genetic background and culture conditions.
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fig1: bnch loss of function alleles are semi-lethal and disrupt a highly conserved predicted anion/sugar permease of the MFS. (A) The genomic bnch locus (52E, 14 kb) encodes at least five alternatively spliced transcripts. Translation initiation and termination sites are indicated in red. The approximate location of the P{lacW}[25/11] insertion and point mutations (11F5, E14.1, N, P) is shown. The extent of small deletions (Δ29, Δ31, Δ86) generated by imprecise P-element excision of P{LacW}[25/11] is indicated. The alleles affect gene regions that are common to all alternatively spliced isoforms. (B) Predicted membrane topology for Bnch showing the 12 transmembrane domains typical for proteins of the MFS. The position of the anion/cation (ACS) domain signature is indicated in red. EMS mutations result in the introduction of stop codons (for 11F5, E14.1, and P) or a nonconservative amino acid change (for N) and their positions in the protein are indicated by asterisks. The position of the N missense mutation is shown in a partial multiple alignment of eukaryotic Bnch proteins and consensus sequences of the ACS and sugar porter (SP) subfamilies. The percentages identity and similarity of eukaryotic Bnch proteins to Drosophila Bnch are given in the table. Number of identified Bnch homologues per species is between parentheses. (C) Complementation analysis of bnch point mutations (11F5, E14.1, N, P), excision alleles (Δ29, Δ31, Δ86), deletions (Δ2B, Jp8) and P-element insertion (25/11) indicates allelism. The P{LacW}[25/11] chromosome and its derivatives contain an unrelated lethal mutation that is uncovered by the Jp8 deficiency. The frequency of homozygous and transheterozygous escapers (in parentheses) is not absolute and strongly dependent on the genetic background and culture conditions.

Mentions: We identified the bnch mutation in an enhancer detector screen for genes expressed in the nervous system (Kania et al., 1995): P{LacW}[25/11] is inserted 19 bp upstream of the transcription start site of CG8428 (Fig. 1 A) (Kania, 1996). Allelic mutations were recently reported as spinster and diphthong (Nakano et al., 2001; Sweeney and Davis, 2002). Using P{LacW}[25/11], we found LacZ expression in a subset of glial cells in the embryonic, larval, pupal, and adult nervous system (unpublished data), similar to enhancer detector-induced LacZ expression patterns reported previously (Nakano et al., 2001). However, using an anti-Bnch antibody in adult wild-type brains, we observed that Bnch expression is enriched in—but not restricted to—glial cells and also present in neurons (unpublished data).


Aberrant lysosomal carbohydrate storage accompanies endocytic defects and neurodegeneration in Drosophila benchwarmer.

Dermaut B, Norga KK, Kania A, Verstreken P, Pan H, Zhou Y, Callaerts P, Bellen HJ - J. Cell Biol. (2005)

bnch loss of function alleles are semi-lethal and disrupt a highly conserved predicted anion/sugar permease of the MFS. (A) The genomic bnch locus (52E, 14 kb) encodes at least five alternatively spliced transcripts. Translation initiation and termination sites are indicated in red. The approximate location of the P{lacW}[25/11] insertion and point mutations (11F5, E14.1, N, P) is shown. The extent of small deletions (Δ29, Δ31, Δ86) generated by imprecise P-element excision of P{LacW}[25/11] is indicated. The alleles affect gene regions that are common to all alternatively spliced isoforms. (B) Predicted membrane topology for Bnch showing the 12 transmembrane domains typical for proteins of the MFS. The position of the anion/cation (ACS) domain signature is indicated in red. EMS mutations result in the introduction of stop codons (for 11F5, E14.1, and P) or a nonconservative amino acid change (for N) and their positions in the protein are indicated by asterisks. The position of the N missense mutation is shown in a partial multiple alignment of eukaryotic Bnch proteins and consensus sequences of the ACS and sugar porter (SP) subfamilies. The percentages identity and similarity of eukaryotic Bnch proteins to Drosophila Bnch are given in the table. Number of identified Bnch homologues per species is between parentheses. (C) Complementation analysis of bnch point mutations (11F5, E14.1, N, P), excision alleles (Δ29, Δ31, Δ86), deletions (Δ2B, Jp8) and P-element insertion (25/11) indicates allelism. The P{LacW}[25/11] chromosome and its derivatives contain an unrelated lethal mutation that is uncovered by the Jp8 deficiency. The frequency of homozygous and transheterozygous escapers (in parentheses) is not absolute and strongly dependent on the genetic background and culture conditions.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171373&req=5

fig1: bnch loss of function alleles are semi-lethal and disrupt a highly conserved predicted anion/sugar permease of the MFS. (A) The genomic bnch locus (52E, 14 kb) encodes at least five alternatively spliced transcripts. Translation initiation and termination sites are indicated in red. The approximate location of the P{lacW}[25/11] insertion and point mutations (11F5, E14.1, N, P) is shown. The extent of small deletions (Δ29, Δ31, Δ86) generated by imprecise P-element excision of P{LacW}[25/11] is indicated. The alleles affect gene regions that are common to all alternatively spliced isoforms. (B) Predicted membrane topology for Bnch showing the 12 transmembrane domains typical for proteins of the MFS. The position of the anion/cation (ACS) domain signature is indicated in red. EMS mutations result in the introduction of stop codons (for 11F5, E14.1, and P) or a nonconservative amino acid change (for N) and their positions in the protein are indicated by asterisks. The position of the N missense mutation is shown in a partial multiple alignment of eukaryotic Bnch proteins and consensus sequences of the ACS and sugar porter (SP) subfamilies. The percentages identity and similarity of eukaryotic Bnch proteins to Drosophila Bnch are given in the table. Number of identified Bnch homologues per species is between parentheses. (C) Complementation analysis of bnch point mutations (11F5, E14.1, N, P), excision alleles (Δ29, Δ31, Δ86), deletions (Δ2B, Jp8) and P-element insertion (25/11) indicates allelism. The P{LacW}[25/11] chromosome and its derivatives contain an unrelated lethal mutation that is uncovered by the Jp8 deficiency. The frequency of homozygous and transheterozygous escapers (in parentheses) is not absolute and strongly dependent on the genetic background and culture conditions.
Mentions: We identified the bnch mutation in an enhancer detector screen for genes expressed in the nervous system (Kania et al., 1995): P{LacW}[25/11] is inserted 19 bp upstream of the transcription start site of CG8428 (Fig. 1 A) (Kania, 1996). Allelic mutations were recently reported as spinster and diphthong (Nakano et al., 2001; Sweeney and Davis, 2002). Using P{LacW}[25/11], we found LacZ expression in a subset of glial cells in the embryonic, larval, pupal, and adult nervous system (unpublished data), similar to enhancer detector-induced LacZ expression patterns reported previously (Nakano et al., 2001). However, using an anti-Bnch antibody in adult wild-type brains, we observed that Bnch expression is enriched in—but not restricted to—glial cells and also present in neurons (unpublished data).

Bottom Line: Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions.Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner.We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT
Lysosomal storage is the most common cause of neurodegenerative brain disease in preadulthood. However, the underlying cellular mechanisms that lead to neuronal dysfunction are unknown. Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions. At the bnch larval neuromuscular junction, we observe similar inclusions and find defects in synaptic vesicle recycling at the level of endocytosis. In addition, loss of bnch slows endosome-to-lysosome trafficking in larval garland cells. In adult bnch flies, we observe age-dependent synaptic dysfunction and neuronal degeneration. Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner. We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

Show MeSH
Related in: MedlinePlus